Poor Man's Matterhorn

[Patrick Bateman]

A few years ago I made an attempt to "reverse-engineer" the Matterhorn. It turns out that a single Matterhorn is capable of absolutely ludicrous levels of output. But IMHO, the size and the price is out of reach of the average 'weekend warrior' that wants to do EDM gigs in the middle of the desert or the forest.

If you'd like to read about that, read this: http://www.diyaudio.com/forums/subwoofers/250032-school-horn-vs-modern-vented-box-post3794298.html

Tom Danley, inventor of the Matterhorn, weighed in here:

http://www.diyaudio.com/forums/subwoofers/250032-school-horn-vs-modern-vented-box-post3794386.html

So I was curious to see what could be possible on a very limited budget. Basically something like the Matterhorn, but small enough to be towed by a truck, a SUV, possibly even a car.

 

[Patrick Bateman]

IMHO, the Harbor Freight 62648 is probably the best foundation of a "Mini Matterhorn." I've owned three different Harbor Freight trailers, and they're REALLY friendly for the DIY crowd:

1) Because you have to build the dumb trailer, you can put one together for about 25% of the cost of a new trailer. It's literally a box of parts. The first one I built took two days, but I could probably build one in an afternoon now.
2) Because you build the trailer, it's conducive to modification

Here's a few pics of the Harbor Freight trailers, in various stages of modification:

An externally hosted image should be here but it was not working when we last tested it.

 

[Patrick Bateman]

In my "guesstimate" of the Danley Matterhorn, it looks like it's capable of about 150dB with an input of 40,000 watts

So the "trick" would be to create something capable of similar output, but with a higher F3. Basically trade low frequency output for efficiency.

Something like a Danley BC218 is an obvious option, but designed so that it's part of a trailer.

IE, a subwoofer that weighs about one thousand pounds, but it's permanently attached to a trailer. Basically hitch it to your SUV and tow it to your desert or forest party. Heck, you could use this for your BBQ if your yard was big enough.

 

[Patrick Bateman]

Here's some dimensions:

A Danley Matterhorn measures 8' x 8' x 20'. That's 1,280 cubic feet. Weight is unknown.

A Danley BC218 measures 5' x 5' x 2.5'. That's 62.5 cubic feet. Weight is 511lbs.

A Harbor Freight trailer is 4' x 8'. If the box is 6' tall, that gives us 192 cubic feet, or more than three times as much space as a Danley BC218.

It's tempting to make the trailer 8' tall, but that would exceed the weight limit of the Harbor Freight trailer.

 

[Patrick Bateman]

Even though this "Mini Matterhorn" is a trailer, weight becomes a problem in a hurry.

The B&C 18NW100 is an obvious candidate; with 2400 watts of power handling it weighs just 24lbs

Here's the frequency response of six of the woofers, with 10,000 watts of power, in a front loaded horn with a volume of 183 cubic feet.

These sims should illustrate how powerful the BC218 is! It's maximum output is about the same, but it's a fraction of the size. But I did something very intentional in this design; it's optimized to trade efficiency for space. IE, it's a much bigger box than the BC218, but I'm using the additional volume to increase the output at very low frequency.

I am also using an 18" woofer that isn't exactly "top of the line." The 18NW100 is a very nice driver, but if you're willing to spend 2-3x as much, you can get more output in a smaller box.

But this box isn't about maximum output in a small box; this box is about maximum output without breaking the bank.

 

[Patrick Bateman]

Here's the specs if you'd like to build it yourself

Here's the schematic. Six woofers, 183 cubic feet. That will fit on a trailer that measures 4' x 8' x 6'

Here's the displacement with 10,000 watts. (1667 watts per woofer.) Due to the low tuning, the woofers are exceeding their xmax by about 25%.

Oddly enough, the solution is to make the box smaller! That would reduce excursion. Another option is to use more woofers, for instance use eight instead of six.

 

[Patrick Bateman]

Here's some quick calculations on the cost:

1) Harbor Freight 4'x8' trailer : $300
2) B&C 18NW100 18" woofer (6) : $1944
3) plywood sheets (10) : $400
4) QSX PLX3102 3200W amplifier (3) : $3180

Total : $5824

 

[Patrick Bateman]

One obvious way to reduce the cost of this "Mini Matterhorn" is to use a cheaper woofer. I'm a big fan of Alpine car subs. Due to economies of scale, it's very difficult to find anything that generates as much output, for as little money, as Alpine car subs.

In this sim, the horn is exactly the same, but instead of using six B&C eighteens, it's using twelve Alpine SWS-15D4s. The Alpines can be found everywhere from Sonic Electronix to Amazon to Wal Mart, and twelve of them cost $780. Six of the B&Cs cost $1944.

The efficiency of the Alpine is a bit lower, because the higher Q of the driver is lowering the F3 of the design.

Here's the excursion of the two designs. It's virtually identical, because the response shape is virtually identical. The Alpine has nearly twice as much xmax : 15mm.

Here's the electrical impedance. The way that I wired the Alpines, their impedance is about 40% lower than the B&C. The Alpines have dual 4 ohm voice coils. So there's a lot of options here.

Here's some quick calculations on the cost:

1) Harbor Freight 4'x8' trailer : $300
2) Alpine SWS-15D4 (12) : $780
3) plywood sheets (10) : $400
4) QSX PLX3102 3200W amplifier (3) : $3180

Total : $4660